The present invention concerns a coating composition for coating a curable layer to a resin substrate and a resin article having optical permeability applied with a curable coating layer by the coating composition.
Plastic molding products have advantages such as reduced weight, impact resistance, dyeability, and fabricability compared with those of glass and have a primary role particularly in the field of lenses such as spectacle lenses and lenses for use in electronic equipments. On the contrary, they are inferior, for example, in view of scratch resistance and heat resistance, and various attempts have been made for improvement and modification for improving such drawbacks. As a method of improving the scratch resistance, a curable coating layer has generally been applied to plastic substrates. The curable layer generally includes a coating composition comprising a hydrolyzate of an organosilane as a main ingredient. Since interference fringes become conspicuous to cause poor appearance when a difference of refractive index relative to a substrate is large, the refractive index is controlled by dispersing fine particles of metal oxides into the coating composition. In recent years, highly refractive substrates have become used for plastic substrates, particularly, in spectacle lens. Techniques of fine particle sols of metal oxides and coating compositions containing them coping with such increase in the refractive index are disclosed, for example, in JP-A Nos. 2001-122621, 2001-123115, 2005-15324, and 2005-15756.
However, in a case of coating the coating compositions as described above to the resin substrates intending for forming the curable layer, adhesion is poor and they are not suitable to practical use both for initial adhesion and weather proof adhesion. Accordingly, it requires a two step process of coating a pre-treatment liquid to a resin substrate for providing adhesion and then coating a coating composition. Particularly, in polycarbonate resin substrates, adhesion is poor and coating of the pretreatment liquid is indispensable. Further, as other feature of the polycarbonate resin, it is difficult to be dyed compared with other resins and, in a case where it is necessary for dyeing such a resin of poor dyeability, it is necessary to make the coating layer dyeable.
Further, JP-A No. 06-256718 discloses a curable layer composition that adheres with a thermoplastic sheet with no application of a pretreatment liquid by incorporating a caprolactone group polyester polyol as an adhesion promoter to a coating composition. However, also the composition is insufficient for adhesion and, when the caprolactone group polyester polyol is incorporated to such an extent as capable of obtaining necessary adhesion, this results in a problem that a resin composite product applied with the curable layer suffers from remarkable whitening. The whitening phenomenon remarkably worsens the performance for products such as optical products, for example, spectacle lenses and application is not possible to those products for which whitening phenomenon is undesirable. In a case of attempting to decrease the amount of the caprolactone group polyester polyol to such an extent as not causing whitening, adhesion is no more obtainable.
The present inventors have previously proposed a coating composition containing a polycarbonate diol for solving the subject described above (pamphlet of WO2005/23946). According to the coating composition, a curable coating layer can be formed with one solution without coating a pretreatment liquid to a resin substrate. However, since the curable coating layer is formed without forming a primer layer by the coating of the pretreatment liquid, in a case where the substrate is a resin difficult to be dyed as a polycarbonate resin, the dyeability has to be provided only by one layer of the curable coating layer. In a case of adding a sufficient amount of a dyeability providing agent to the coating composition intending for providing a dyeability at a practical level by only one curable coating layer, adhesion of the curable coating layer after dyeing or adhesion after conducting salt water boiling test was worsened extremely.    Patent Document 1: JP-A No. 2001-122621    Patent Document 2: JP-A No. 2001-23115    Patent Document 3: JP-A No. 2005-15324    Patent Document 4: JP-A No. 2005-15756    Patent Document 5: JP-A No. 06-256718    Patent Document 6: pamphlet WO2005/23946